Important documents, such as tax returns, notices and checks are usually sent with a return receipt requested, which is confirmation that a letter was received. However, acknowledgment that something was received, such as a sealed letter, is not proof as to the contents of the letter.
There is therefore a substantial need for proof of delivery for the contents of a mailing. This would require that a copy be reproduced or provided of a handwritten, typed, printed or electronic material forwarded to another party.